1. Field of the Invention
The present invention relates to a magnetron used in microwave applications such as a microwave oven and a method of manufacturing an anode vane of the magnetron.
2. Description of the Related Art
FIG. 12 is a cross-sectional view illustrating a schematic structure of a known magnetron. In addition, FIG. 13 is a partial sectional perspective view illustrating an assembly state of the anode structure of the magnetron shown in FIG. 12. In FIGS. 12 and 13, a plurality of anode vanes 2 are brazed on an inner peripheral surface of an anode cylinder 1 by a high melting point brazing material 3 and are protruded toward a central axis of the anode cylinder 1. In the anode vanes 2, two large and small concentric strap rings 4a and 4b are alternately brazed on an upper end and a lower end thereof. In addition, in at least one of the anode vanes 2, a concave groove 5 is formed, and one end part of a microwave guide-out conductor 6 having a rod shape is brazed in the groove 5. In the one end part of the microwave guide-out conductor 6, a concave groove 7 (see FIG. 13) is formed, and the concave groove 7 is engaged with the concave groove 5. Since the plurality of the anode vanes 2 are formed in the same shape, the anode vanes 2 are arranged by alternately changing each direction thereof as much as 180 degrees so that the strap rings 4a and 4b are alternately brazed. Specifically, as shown in FIG. 13, the anode vane 2 of the front side is disposed so that the concave groove 5 faces downward, and the anode vane 2 of the back side is disposed so that the concave groove 5 faces upward. As described above, the anode vanes 2 are arranged by alternately changing each direction thereof.
The plurality of the anode vane 2 are arranged radially in the anode cylinder 1, and a cavity resonator is formed in an area surrounded by the anode vanes 2 neighboring to each other and the anode cylinder 1.
In a manufacturing process of the known magnetron mentioned above, by using the high melting point brazing material 3, the plurality of anode vanes 2 are brazed on the inner peripheral surface of the anode cylinder 1, the strap rings 4a and 4b are brazed to the anode vane 2, and the microwave guide-out conductor 6 is brazed to at least one anode vane 2, simultaneously. In this process, as shown in FIG. 14, sometimes, an excess portion of a brazing material 3a formed in a brazing process (hereinafter, it is referred to as a residual brazing material) may spread over a side face of the anode vane 2 or flow in the strap ring 4a side. When inflow amount of the residual brazing material 3a is large, it is difficult to obtain a stable resonating operation in a predetermined mode. Particularly, when the brazing material which is spread over the side face of the anode vane 2 connected to the microwave guide-out conductor 6 is protruded to an adjacent anode vane 2 side, there is a concern about local chaos in electric field caused by focusing high frequency electric field thereon. In addition, there are a lot of cases where amount of the residual brazing material 3a is different for each anode vane 2, and thus the non-uniformity thereof have a great adverse effect on a resonant frequency.
To solve the problems mentioned above, in Patent Document 1, a brazing material inducing groove is provided on the side face of the anode vane having a plate shape protruded from the brazing portion formed on the inner peripheral surface of an anode cylinder to the center of the anode cylinder, and is extended in the range from a brazing portion of an anode cylinder at least to a groove for inserting the microwave guide-out conductor. By providing the brazing material inducing groove, the residual of the melted brazing material is guided into the inducing groove when the anode vane is brazed to the anode cylinder. Therefore, it is possible to prevent the brazing material from being spread lower than the inducing groove.
Patent Document 1: Japanese Unexamined Patent Application Publication No, H01-95442
Although the brazing material inducing groove is provided on the side face of the anode vane toward the central axis, sometimes the residual brazing material may spread from the brazing portion of the anode cylinder of a lower side of the groove in the central axis direction of the anode vane, or may overflow from the groove to the lower side of the anode vane. Thus, there is a concern about occurrence of non-uniformity in characteristics, that is, non-uniformity in the resonant frequency. Inventors of the invention found the fact that the resonant frequency is greatly affected when the residual brazing material spread to a part of the front end of the anode vane. Accordingly, as shown in FIG. 15, it is necessary to configure the residual brazing material as not to spread to the front end part 2a of the anode vane 2.